The present invention is directed to a hip socket joint for cement-free anchoring in the pelvis and it includes a rigid outer member and a socket member secured within the outer member.
In implants in the human body, generally the volume of the foreign member positioned within the tissue of the human body is kept as small as possible. As a result, artificial joint sockets include relatively thin-walled socket members and, due to the sliding characteristics of the socket members frequently made of plastic, particularly polyethylene, the socket members are relatively resilient and transfer the pelvic movements to the sliding surfaces which are in engagement with one another. Such movements lead to the so-called "cherry-stone" effect wherein a solid core member works itself out of the softer material during relative movement. Since the socket members are formed of plastics material they tend to experience plastic deformations under continuous stresses and such deformations tend to result in changes in the socket surfaces. Accordingly, the interengagement of the socket surface which forms one of the sliding surfaces of the joint with the other sliding surface formed by the joint head or member is disturbed and leads to increased abrasion.
Therefore, it is a primary requisite that the hip joint socket as a whole is as strong and rigid as possible so that it does not deform during movement of the joint. This requirement has led to a plurality of different sockets in which a socket member is enclosed within and held by an outer member, note German Offenlegungsschrift No. 29 50 536. While this arrangement protects the socket member against the direct influence of pelvic movements, there is the problem, particularly during plastic cold flow of a plastics material socket member, that relative movement takes place between the socket member and its outer member which leads to wear and abrasion between the sliding surfaces. Moreover, a shell-shaped outer member enclosing the socket member represents a large foreign mass within the human body.